Bituminous compositions



3,070,455 BI'IUMINGUS COMPGSITIONS Stephen H. Alexander, El Dorado, Ark., assignor to Monsanto Chemical Company, St. Louis, Mo, a corporation of Delaware No Drawing. Filed June 22, 1959, Ser. No. 821,715 4 Claims. (Cl. 106-278) This invention relates to bituminous compositions and more particularly to improved asphaltic coating compositions and the application of such compositions to metallic surfaces.

Cathodic protection is a widely used method for decreasing the rate of corrosion of metallic surfaces which are exposed to electrolytes. Cathodic protection is well described in the art and comprises the use of an impressed current to prevent or reduce the rate of corrosion of a metal in an electrolyte by making the metal the cathode for the impressed current.

While cathodic protection can be and is employed on a wide variety of metallic surfaces or structures, it is particularly well suited for the protection of metal pipes installed or buried beneath the surface of the earth. A heavy current demand results when cathodic protection is employed on bare metal surfaces. Therefore, as a general rule, underground pipes and other metallic surfaces are protected by both a protective coating and by cathodic protection. Bituminous compositions, of either coal tar or petroleum origin, have become widely used as protective coatings for metallic surfaces. It has been found, however, that such coating compositions have a tendency to disbond from the metal surface when the coated metal surfaces are subjected to cathodic protection. This disbonding is emphasized, seriously so, in the areas of any holidays or breaks in the protective coating.

It is an object of this invention to provide an improved bituminous coating for metallic surfaces which are to be subjected to cathodic protection. It is also an object of this invention to provide an improved process for protecting metal surfaces which are to be subjected to cathodic protection. Other objects will become apparent from the description of this invention.

When using bituminous protective coatings which are designed for application at elevated temperatures, it is necessary that the metallic surface first be given a prime coat. This is generally a cutback bitumen applied at ambient temperatures. After the prime coat has set, the finish coat is applied, generally at elevated temperatures. It has now been discovered that the disbonding of a bituminous coating composition from a metal surface under cathodic protection can be either prevented or significantly retarded by incorporating into the cutback bitumen prime coat a minor amount of an imidazolinium chloride having the formula:

(I) N--H= wherein R represents an alkyl or alkenyl radical containing from to 20 carbon atoms. According to a preferred embodiment of this invention, an improved asphaltic prime coat for metallic surfaces is provided comprising a liquid hydrocarbon vehicle, an asphalt and a minor amount of an imidazolinium chloride as hereinbefore described. Substantially improved protection of metallic surfaces subjected to cathodic protection is achieved by applying to said metallic surface a prime coat as above described and then a finish asphalt coat of the type well known to those skilled in the art.

3,070,455 Patented Dec. 25, 1962 To illustrate this invention, a cutback asphalt primer was prepared using 40% by weight of an airblown petroleum asphalt having a softening point of 195 F. and a penetration of 7 mm./l0 at 77 F. and 60% by Weight of a petroleum naphtha having a boiling range of 300 to 360 F. The primer had a viscosity of 40 Saybolt Furol seconds at 77 F.

The finish asphalt coating was prepared by mixing from 19 to 21% by weight of total composition of slate flour having a fineness such that at least passed through a 325 mesh sieve with an airblown asphalt having a softening point of 228 to 234 F. and a penetration of 7 to 9 mm./ 10 at 77 F. The finish coat had a viscosity of approximately 900 Saybolt Furol seconds at 375 F.

A clean set of metal panels were then brush coated with the primer as above described. Another set of clean metal panels were brush coated with the primer as above decribed to which had been added 1% by weight of total composition of an imidazolinium chloride of the Formula I hereinbefore set forth wherein R was a normal heptadecenyl radical. Another set of clean metal panels were brush coated with the primer as above described to which had been added 1% by weight of total composition of a mixture of imidazolinium chlorides of the Formula I hereinbefore set forth wherein R was a normal undecyl, tridecyl, pentadecyl and heptadecyl radical. The panels were allowed to dry overnight and then a 5565 mil coating of the finish coat as above described was applied at 450 to 460 F. using a plaquing machine.

After the panels were dry, an intentional holiday was punched into the surface of each coated panel and the panel immersed in an electrolyte having the following composition.

Compound: G./l. of solution Magnesium chloride hexahydrate 11.0 Calcium chloride 1.2 Sodium sulfate 4.0

Sodium chloride 25.0

The specimens were placed under cathodic protection with sufiicient current being drained to the specimens to maintain a saturated calomel potential of 1.5 volts. After seven days the specimens were removed and examined for disbonding. Disbonding was significantly reduced on those panels which had first been primed using the novel coating of this invention.

The origin of the bitumen used in preparing the novel prime coat of this invention is not a critical factor. It may be coal tar or petroleum asphalt. Preferred prime coats of this invention utilize a petroleum asphalt having a softening point of F. to 250 F. and a penetration of 0 to 25 mm./ 10 at 77 F. The bitumen content of the prime coat can vary but preferably it is maintained in the range of 35% to 55% by weight of total composition. The liquid hydrocarbon vehicle can also vary in composition and conventional vehicles well known to those skilled in the art can be used. Hydrocarbons boiling in the range of 200 to 400 F. are particularly preferred.

Any of the imidazolinium chlorides having the Formula I hereinbefore set forth can be used to prepare the prime coats of this invention. Typical of those can be used are those having the Formula I wherein R represents the decyl, decenyl, undecyl, undecenyl, dodecyl, dodecenyl, tridecyl, tridecenyl, tetradecyl, tetradecenyl, pentadecyl, pentadecenyl, hexadecyl, hexadecenyl, heptadecyl, octadecyl, octadecenyl, nonadecyl, nonadecenyl, eicosane and eicosene radical. The hydrocarbon radical represented by R can be normal or branched, the former being preferred. Only a minor amount of this additives is required to realize the benefits of this invention. Preferred prime coats of this invention contain from about 0.05 to 5.0% by weight of total composition of the additive.

Any conventional bituminous finish can coat be used with, the novel primer of this invention. Again, the bitumen can be coal tar or petroleum asphalt. The finish coat can contain various fillers and additives, such as are usually found in the generally used coating compositions.

What is claimed is:

1. An improved prime coat for metallic surfaces which are to be coated with a finish bituminous protective coating and then subjected to cathodic protection, consisting essentially of a bitumen, a liquid hydrocarbon vehicle and from 0.5% to 5.0% by weight of total composition of an imidazolinium chloride having the formula IfiT-CH1 R-C\ /J3H:

If :Oornot CH1 CHaOH wherein R represents a radical selected from the group consisting of alkyl and alkenyl radicals containing from to 20 carbon atoms.

2. An improved prime coat for metallic surfaces which are to be coated with a finish bituminous protective coating and then subjected to cathodic protection, consisting essentially of a liquid hydrocarbon vehicle, petroleum asphalt and from 0.5% to 5.0% by weight of total composition of an imidazolinium chloride having the formula wherein R represents a radical selected from the group consisting of alkyl and alkenyl radicals containing from 10 to 20 carbon atoms.

3. The prime coat of claim 2 wherein the petroleum asphalt has a softening point of to 250 F. and a pen- CHzOH wherein R represents a radical selected from the group consisting of alkyl and alkenyl radicals containing from 10 to 20 carbon atoms, and thereafter coating said surfaces with a finish bituminous protecting coating.

References Cited in the file of this patent UNITED STATES PATENTS 2,468,163 Blair Apr. 26, 1949 2,685,523 Cross Aug. 3, 1954 2,860,996 Furey Nov. 18, 1958 2,950,211 Huber et al Aug. 23, 1960 

1. AN IMPROVED PRIME COAT FOE METALLIC SURFACES WHICH ARE TO BE COATED WITH A FINISH BITUNINOUS PROTECTIVE COATING AND THEN SUBJECTED TO CATHODIC PROTECTION, CONSISTING ESSENTIALLY OF A BITUMEN, A LIQUID HYDROCARBON VEHICLE AND FROM 0.5% TO 5.0% BY WEIGHT OF TOTAL COMPOSITION OF AN IMIDAXOLINIUM CHLORIDE HAVING THE FORMULA WHEREIN R REPRESENTS A RADICAL SELECTED FROM THE GROUP CONSISTING OF ALKYL AND ALKENYL RADICALS CONTAINING FROM 10 TO 20 CARBON ATOMS. 